Energy efficient role of Ni/NiO in PdNi nano catalyst used in alkaline DEFC

Abstract

The present investigation is based on a study of electro-oxidation of ethanol in alkaline medium over the carbon supported Pd_xNi_y catalyst formulations synthesized by simultaneous reduction of the precursors using sodium borohydride as the reducing agent. X-ray diffraction studies of the PdNi/C nano-particles reveal formation of the face-centered cubic crystalline Pd, NiO and Ni(OH)₂ on a meso porous carbon support whereas XPS confirmed the presence of metallic Ni and the oxide phases NiO, Ni(OH)₂, NiOOH in the catalyst matrix. The structure and morphology of the binary matrix and the role of Ni and its oxide as a catalytically contributing entity in the oxidation process was ascertained by the help of respective analytical techniques like transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), voltammetry and chronoamperometry. Sequential oxidation steps were suggested involving dimeric (NiO)₂ as one of the intermediate species during the oxidation reaction proceeding towards aldehyde formation and further to carbonate production via the intermediate formation of a six member ring, thereby increasing the reaction rates. This phenomenon has been discussed at molecular level using the results obtained from XPS analysis. The observations were further accomplished by extending the work to ion chromatography for quantitative analysis of the products formed during oxidation of ethanol. All the above results are congruent with the mechanistic interpretation and reflect the paramount significance of NiO existing in the binary catalyst matrix for accelerating ethanol oxidation reaction kinetics at a temperature 40 °C and above.